Holographic Dark Energy in Braneworld Models with Moving Branes and the w=-1 Crossing

We apply the bulk holographic dark energy in general 5D two-brane models. We extract the Friedmann equation on the physical brane and we show that in the general moving-brane case the effective 4D holographic dark energy behaves as a quintom for a large parameter-space area of a simple solution subclass. We find that $w_\Lambda$ was larger than -1 in the past while its present value is $w_{\Lambda_0}\approx-1.05$, and the phantom bound $w_\Lambda=-1$ was crossed at $z_{p}\approx0.41$, a result in agreement with observations. Such a behavior arises naturally, without the inclusion of special fields or potential terms, but a fine-tuning between the 4D Planck mass and the brane tension has to be imposed.